man: document tmpfiles.d/ user/group resolvability needs

diff --git a/man/tmpfiles.d.xml b/man/tmpfiles.d.xml
index 67bd1dc7243b9851e4c68b61e3daa192396b2c0e..ac6565ec93cb62a4f7aa5b8a5c20c78a7232fc71 100644 (file)
--- a/man/tmpfiles.d.xml
+++ b/man/tmpfiles.d.xml
@@ -495,6 +495,14 @@ w- /proc/sys/vm/swappiness - - - - 10</programlisting></para>
       lines, when omitted or when set to <literal>-</literal>, the file ownership will not be modified. These
       parameters are ignored for <varname>x</varname>, <varname>r</varname>, <varname>R</varname>,
       <varname>L</varname>, <varname>t</varname>, and <varname>a</varname> lines.</para>
+
+      <para>This field should generally only reference system users/groups, i.e. users/groups that are
+      guaranteed to be resolvable during early boot. If this field references users/groups that only become
+      resolveable during later boot (i.e. after NIS, LDAP or a similar networked directory service become
+      available), execution of the operations declared by the line will likely fail. Also see <ulink
+      url="https://systemd.io/UIDS-GIDS.html#notes-on-resolvability-of-user-and-group-names">Notes on
+      Resolvability of User and Group Names</ulink> for more information on requirements on system user/group
+      definitions.</para>
     </refsect2>
 
     <refsect2>